Present invention relates to an analysis equipment of sample, more in detail, relates to a crystal defect measurement method and equipment using the same for measuring crystal defect such as sludge or stacking fault in a semi-conductor wafer, especially a silicon wafer.
According to the improvement of integration degree of large scale integrated circuit (LSI), degradation of non-defective unit acquisition rate and reliability caused by failure of the metal oxide semiconductor (MOS) transistor which constitutes the large scale integrated circuit, becomes a big problem recently.
As possible cause of failure of metal oxide semiconductor transistor, breakdown of a gate oxide junction and leak electric current in a connected part are typical. Most of the failure of these metal oxide semiconductor transistor are originated in crystal defect in a silicon substrate.
That is, in the large scale integrated circuit manufacturing process, when the crystal defect exists in a near surface region of the silicon substrate converted into the silicon oxide by oxidation, construction defect is formed in a silicon oxide layer, and the breakdown occurs in the large scale integrated circuit operation.
Moreover, leak current occurs abundantly when the crystal defect exists in a depletion layer of the connection part.
When the crystal defect is formed in the near surface region where element is formed in silicon substrate, and it is not desirable, because failure of metal oxide semiconductor transistor occurs, and in this way, the defect measurement is important in a quality control of silicon single crystal.
As conventional method to measure such a defect, there is a method mentioned in Mat. Res. Soc. Symp. Proc. Vol. 442 1997 Materials Research Society, pages 37 to 42.
In this reference, a method is shown in which two light beams having different wavelength which penetration depth thereof for a silicon wafer are different three times or more each other, are irradiated slantingly on the sample surface by a slantingly incident optical system, and a scattering light from a crystal defect is detected on a vertical direction of a surface of said sample.
According to this method, the depth of the crystal defect can be known from a ratio of a scattering light intensity of a short wavelength and a scattering light intensity of a long wavelength, and size of the crystal defect can be known from the scattering light intensity of the long wavelength.
In this way according to the measurement method adopting the slantingly incident optical system, when the light beam diameter to be irradiated is squeezed to be small, irradiation position of the light beam moves up and down according to flatness irregularity of the wafer and problem on accuracy of the sample movement stage.
Because of this moving up and down, the irradiation position of the slantingly incident light beam is moved on the sample surface to a direction parallel to the sample surface.
When the irradiation beam is irradiated with an angle Brewster angle of silicon (75.degree.) and the surface height of the wafer is moved 0.5 .mu.m as stated above, the beam irradiation position moves about 1.9 .mu.m on the wafer surface. Moreover because of the moving up and down identically, detection position of the detection system changes up and down, and an accurate scattering light signal strength is not provided.
Therefore, it becomes important that a relative position of a beam irradiation region and a detection region is kept to be constant, and a distance of them from the sample is kept to be constant.
As an example of the control system of the irradiation or detection system, Japanese Patent Laid-open No. 8-75980 bulletin is published.
In this bulletin, for an object of image observation, an objective lens or a sample stage of an optics type microscope is moved up and down so as to make the contrast high. In an irradiation optical system (lighting object), a uniform lighting is suitable in order to observe the image with a high contrast, when it is irradiated through an objective lens or when it is irradiated from a bottom of the sample stage, and there is no need to pay any special attention.
On the other hand, in the crystal defect analysis equipment, a spot diameter of the irradiation light is enough smaller than a visual field of the objective lens, and moreover because irradiation light is slantingly incident, the irradiation position on the sample surface is changed according to up and down drift of the sample surface.
Therefore, the irradiation system needs to be controlled precisely.
There is a technique shown in Japanese Patent Laid-open No. 8-96738 bulletins as an example of a focal point matching system of a scan type electron microscope.
That is, a probe light source for the focal point matching is provided, and a gravity position of a reflected light from the sample surface is detected by a position sensor, the focal point position is changed by changing an exciting current value of the objective lens.
In the crystal defect measurement equipment, it is equivalent for aligning only the irradiation system, it is different from controlling the objective lens of the detection system.